THE FAR-INFRARED-RADIO CORRELATION AT HIGH REDSHIFTS: PHYSICAL CONSIDERATIONS AND PROSPECTS FOR THE SQUARE KILOMETER ARRAY

Journal Article · Fri Nov 20 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/706/1/482· OSTI ID:21378175

I present a predictive analysis for the behavior of the far-infrared (FIR)-radio correlation as a function of redshift in light of the deep radio continuum surveys which may become possible using the Square Kilometer Array (SKA). To keep a fixed ratio between the FIR and predominantly non-thermal radio continuum emission of a normal star-forming galaxy, whose cosmic-ray electrons typically lose most of their energy to synchrotron radiation and inverse Compton (IC) scattering, requires a nearly constant ratio between galaxy magnetic field and radiation field energy densities. While the additional term of IC losses off of the cosmic microwave background (CMB) is negligible in the local universe, the rapid increase in the strength of the CMB energy density (i.e., approx(1 + z){sup 4}) suggests that evolution in the FIR-radio correlation should occur with infrared (IR; 8-1000 mum)/radio ratios increasing with redshift. This signature should be especially apparent once beyond z approx 3 where the magnetic field of a normal star-forming galaxy must be approx50 muG to save the FIR-radio correlation. At present, observations do not show such a trend with redshift; z approx 6 radio-quiet quasars appear to lie on the local FIR-radio correlation while a sample of z approx 4.4 and z approx 2.2 submillimeter galaxies exhibit ratios that are a factor of approx2.5 below the canonical value. I also derive a 5sigma point-source sensitivity goal of approx20 nJy (i.e., sigma{sub rms} approx 4 nJy) requiring that the SKA specified sensitivity be A{sub eff}/T{sub sys} approx 15,000 m{sup 2} K{sup -1}; achieving this sensitivity should enable the detection of galaxies forming stars at a rate of approx>25 M{sub sun} yr{sup -1}, such as typical luminous infrared galaxies (i.e., L{sub IR} approx> 10{sup 11} L{sub sun}), at all redshifts if present. By taking advantage of the fact that the non-thermal component of a galaxy's radio continuum emission will be quickly suppressed by IC losses off of the CMB, leaving only the thermal (free-free) component, I argue that deep radio continuum surveys at frequencies approx>10 GHz may prove to be the best probe for characterizing the high-z star formation history of the universe unbiased by dust.

• OSTI ID: 21378175
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 706; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BREMSSTRAHLUNG
CORRELATIONS
COSMIC RADIATION
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
EMISSION
ENERGY DENSITY
EVOLUTION
FERMIONS
FREQUENCY RANGE
GALACTIC EVOLUTION
GALAXIES
GHZ RANGE
GHZ RANGE 01-100
IONIZING RADIATIONS
LEPTONS
MAGNETIC FIELDS
MICROWAVE RADIATION
POINT SOURCES
QUASARS
RADIATION SOURCES
RADIATIONS
RED SHIFT
RELICT RADIATION
STARS
SYNCHROTRON RADIATION
UNIVERSE
VISIBLE RADIATION